Volume 412, Number 1, December II 2003
|Page(s)||175 - 184|
|Section||Interstellar and circumstellar matter|
|Published online||25 November 2003|
A massive disk/envelope in shocked H2 emission around an UCHII region
Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 7150-462 Porto, Portugal
2 Instituto Superior da Maia, Av. Carlos Oliveira Campos, 4475-690 Avioso S.Pedro, Portugal
3 Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS-78 Cambridge, MA 02138, USA
4 Joint Astronomy Center, 660 N. A'ohōkū Place, University Park, Hilo, HI 96720, USA
5 Instituto de Astronomia, UNAM-Morelia, Apartado postal 3-72, CP 58090 Morelia, Michoacan, Mexico
Corresponding author: M. S. N. Kumar, firstname.lastname@example.org
Accepted: 2 September 2003
A multi-wavelength study of IRAS 07427–2400 in line and continuum emission was conducted to investigate the nature of a H2 –0 S(1) line emitting feature around this ultra-compact HII region. High resolution 3.6 cm continuum observations from the Very Large Array and 350 μm continuum observations from the Caltech Submillimeter Observatory, combined with archival far-infrared data of IRAS 07427–2400 show a flux density distribution indicating a luminous () point source associated with an ultra-compact HII region. A Grey body model fit to the flux density distribution yields a dust emissivity index () indicative of a circumstellar disk/envelope. Our C18O map shows a dense core centered on the continuum source, with the major axis roughly aligned with the H2 feature. A position-velocity diagram of the C18O core obtained along the major axis shows rotation with a velocity gradient of ~0.1 km s-1 arcsec-1. New CO –2 maps of the region are presented which reveal a massive molecular outflow from the IRAS source. We argue that the H2 feature arises in a disk/envelope around IRAS 07427–2400 and not in an outflow. We present a near-infrared HK band spectrum of the H2 features that shows several ro-vibrational emission lines of H2 and [FeII]. Analysis of the line ratios indicates that the line emission is shock-excited and not due to fluorescence. We estimate an excitation temperature of ~1600 K and an average extinction of mag to the H2 feature. The line fluxes yield a mass accretion rate of yr-1 and a lifetime of ~53601200 yr resulting in a disk/envelope mass of 14050 . The resulting Jeans Mass of 2420 indicates that the disk/envelope will not undergo fragmentation. IRAS 07427–2400 represents one of the most massive YSOs known to date forming by means of accretion.
Key words: stars: formation / accretion: accretion disks / interstellar medium: jets and outflows / ISM: HII regions
© ESO, 2003
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